Organic matter mineralization in intertidal sediments along an estuarine gradient

Abstract

A seasonal study of organic matter mineralization rates was made at 8 intertidal stations in the Westerschelde Estuary (The Netherlands). Organic matter mineralization rates, based on the gaseous emission of carbon dioxide and methane, showed significant dynamic temporal and spatial variability at various scales. Annual rates of organic matter mineralization varied from 8 to about 339 m01 C m-2 yr-l. The temperature dependence of organic matter degradation was described using an Arrhenius-type equation. Activation energies ranged from 54 to 125 kJ mol-' and correlated negatively with depth-integrated rates of mineralization. Spatial differences in mineralization were mainly due to differences in the lability of the organic matter, since the quantity of organic matter was similar between stations on an area1 or volume basis. Average first-order decomposition rate constants ranged from 0.2 to 7 yr-' and decreased towards the seaward end of the estuary due to ageing of riverinederived material. Intertidal sediments were estimated to account for about 25% of the total carbon retention in the Westerschelde estuary. KEY WORDS: Organic matter. Mineralization lntertidal sediments. Estuary. Methane .

Electron donors and acceptors influence anaerobic soil organic matter mineralization in tidal marshes

“…The number of previous studies on this topic is limited, and they report equivocal results. One study along an estuarine gradient in the Netherlands determined that anaerobic organic carbon mineralization was greater in wetlands dominated by methanogenesis than in marine-influenced environments with abundant SO 4 2À (Middelburg et al, 1996). Similarly, mineralization of barley and diatom particles under sulfate-reducing conditions was greater than, or equal to, mineralization under denitrifying conditions (Kristensen and Holmer, 2001).…”

Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)

“…In November 2002 and April 2003, Barró n and Duarte (unpublished data) measured benthic mineralization rates in subtidal areas of the Scheldt estuary using the O 2 incubation method. These values correspond, on average, to 20% of intertidal CR rates measured by Middelburg et al (1996) in 1991, based on CO 2 and methane (CH 4 ) fluxes, during the same periods of the year. As subtidal CR data from Barró n and Duarte do not cover an annual cycle, subtidal mineralization was assumed to represent 20% of intertidal rates derived from the annual values of Middelburg et al (1996).…”

“…These values correspond, on average, to 20% of intertidal CR rates measured by Middelburg et al (1996) in 1991, based on CO 2 and methane (CH 4 ) fluxes, during the same periods of the year. As subtidal CR data from Barró n and Duarte do not cover an annual cycle, subtidal mineralization was assumed to represent 20% of intertidal rates derived from the annual values of Middelburg et al (1996). The percentage of area covered by the intertidal flats was estimated by a bathymetric study in each box (40%, 23%, and 17% in the inner, middle, and outer boxes, respectively).…”

“…Using the incubation method, analytical errors based on at least triplication in the planktonic compartment and SD provided by Middelburg et al (1996) and Barranguet et al (1998) were considered, as well as errors attributed to the averaging of two stations to compute rates for the inner estuary and the averaging to compute either annual or June to December values.…”

“…1). As no benthic measurements were performed during the whole annual cycle, NEP based on in situ incubations was estimated using planktonic metabolism results detailed above and published benthic intertidal metabolic rates (Middelburg et al 1996;Barranguet et al 1998). Planktonic GPP, CR, and NIT rates in the inner box were estimated by averaging results obtained at salinities 2 and 10, and in the middle and outer boxes results obtained at salinity 18 and 25 were used, respectively.…”